Segmental variation in the in vitro cell metabolism of nucleus pulposus cells isolated from a series of bovine caudal intervertebral discs.

Abstract

This study focuses on the association between cell metabolism and molecular matrix composition of nucleus pulposus (NP) tissue with spine level in sequential bovine caudal intervertebral discs. To explore the hypothesis that the molecular composition of NP tissue and corresponding cell metabolism varies with caudal spine. A secondary hypothesis is tested that potential cellular differences are maintained after monolayer culture. In articular cartilage, cell metabolism and molecular matrix composition are influenced by loading history. This may also be a feature of intervertebral discs in series. NP cells (nonpooled or level pooled) were isolated from four sequential bovine caudal intervertebral discs (levels 3-4, 4-5, 5-6, and 6-7) and cultured in alginate beads immediately or following monolayer culture. Levels of 3H-TdR (proliferation) and 35SO4 (GAG synthesis) incorporation were determined from 14 animals. In a separate set of 6 animals, total content of water, DNA, collagen (and type), GAG (and type) were also determined. The rate of 3H-TdR and 35SO4 incorporation in freshly isolated NP cells increased nonlinearly from level 3-4 to 6-7 (P < 0.05). Monolayer cultured cells retained level-specific differences for 35SO4 and 3H-TdR incorporation similar to that of freshly isolated cells. GAG content and chondroitin sulfate proportion decreased distally (P < 0.05); however, total collagen and Type I proportion increased distally (P < 0.05). No significant differences in water or DNA content could be determined. The results support the hypothesis that level-specific differences in NP cell metabolism and molecular composition are dependent on spine level potentially reflecting subtle mechanical differences between levels. Retention of level-specific differences in monolayer may suggest a certain level of cell "programming." This may be important for cellular strategies to repairspecific sites of degeneration.